To start downgrading your operating system you'll need your Black Berry, windows based (sorry mac users; get Bootcamp), and a USB cable to complete the downgrade process.
Note: "App" or "JVM" might appear before an error message (e.g. What you can do: The error ID 35005 is encountered when trying to download or upgrade an application on the Black Berry Play Book tablet.
To revert your Black Berry 10 device to a public OS release, follow the steps outlined in this Knowledge Base Article.
Using Black Berry Link, you will be able to reload your device software to a full OS and, if needed, download any OS updates from your carrier.
Note: "App" or "JVM" might appear before an error message (e.g. What you can do: JVM Errors are raised by the Black Berry Device Software during various activities to make the Black Berry smartphone user aware of a failure in which the Black Berry smartphone could not safely recover normal operation.
You may attempt to load the latest Dev Alpha B update onto your Dev Alpha A, however the Dev Alpha A is no longer officially supported as of 10.1.0.1485.